1. Field of the Invention
The present invention relates to a battery charger and a battery charging method for charging a battery and particularly relates to a battery charger and a battery charging method suited for charging a battery, such as a nickel metal hydride battery, which generates a large amount of heat while being charged.
2. Discussion of the Prior Art
Presently, a chargeable battery which can be repeatedly used for the power supply of, for example, a power tool is used. A nickel cadmium battery is popular as a battery for the power tool, and a battery charger for quickly charging the battery by applying high current thereto is used. Specifically, the battery is quickly charged in about 20 minutes and a power tool can be continuously used by switching to a battery that has been charged.
The inventor of the present invention studied improving the performance of a power tool by using a nickel metal hydride battery as a battery therefor. Although the nickel metal hydride battery has an increased charge storage capacity compared to a nickel cadmium battery, it generates high heat while being charged. If the temperature of the battery becomes high due to the generated heat, the electrodes and separators of the cells within the battery will deteriorate and battery life is shortened. Due to this, it has been impossible to quickly charge the nickel metal hydride battery with high current in a manner similar to the nickel cadmium battery stated above.
Further, the nickel metal hydride battery is less resistant against overcharge than the nickel cadmium battery. If overcharged, the battery life is shortened. It is, therefore, necessary to avoid overcharge.
Considering this, the inventor of the present invention contrived a method of controlling charging current and detecting the completion of charge based on a map for determining a current value based on the absolute temperature of the battery and a temperature rise value. With this method, however, if the number of battery cells in a battery pack increases, a battery cell positioned on the end portion of the battery pack tends to be cooled and that on the central portion thereof is difficult to cool, with the result that the completion of charge cannot be detected based on the battery temperature. Furthermore, if the temperatures of the cells in the battery pack become increasingly irregular, the life of a high temperature cell is shortened and the high temperature cell is difficult to charge. Due to this, the capacities become unbalanced among the cells and it may occur that there is a cell charged 100% and one charged 90% (high temperature cell). Here, if the capacity of the battery pack is used up to 90%, some cells have a residual capacity of 10% and the others have a residual capacity of 0% (high temperature cell). The cells of 0% residual capacity are reverse-charged by those of 10% residual capacity and the battery life is considerably shortened.
The present invention has been made to solve the above-stated problems and an object of this invention is to provide a battery charger and a battery charging method capable of appropriately charging a battery in a short time while avoiding overheating the battery during charging.
In one embodiment of the present invention, a battery charger comprises:
a temperature detecting section for detecting a present battery temperature;
a temperature rise value outputting section for obtaining a temperature rise value from the temperature detected by said temperature detecting section;
a current value retrieving section for retrieving a current value with which the temperature rise value outputted from said temperature rise value outputting section is constant; and
a charge control section for charging a battery with the current value retrieved by said current value retrieving section.
In another embodiment of the present invention, a battery charger comprises:
a storage device storing a target temperature value which a battery temperature is intended to reach;
a temperature detecting section for detecting a present battery temperature;
a temperature gradient calculating section for calculating a temperature rise gradient from charging time based on a difference between a battery temperature at the beginning of battery charge and said target temperature value held by said storage device;
a temperature rise value outputting section for obtaining a temperature rise value from the temperature detected by said temperature detecting section;
a current value retrieving section for retrieving a current value with which the temperature rise value outputted from said temperature rise value outputting section becomes said temperature rise gradient; and
a charge control section for charging the battery with the current value retrieved by said current value retrieving section.
In another embodiment of the present invention, a battery charger comprises:
a storage device storing a target temperature value which a battery is intended to reach;
a temperature detecting section for detecting a present battery temperature;
a temperature rise pattern retrieving section for retrieving a temperature rise pattern for completing battery charge at said target temperature value based on a difference between a battery temperature at the beginning of the battery charge and said target temperature value held by said storage device;
a temperature rise value outputting section for obtaining a temperature rise value from the temperature detected by said temperature detecting section;
a current value retrieving section for retrieving a current value with which the temperature rise value outputted from said temperature rise value outputting section becomes said temperature rise pattern; and
a charge control section for charging the battery with the current value retrieved by said current value retrieving section.
In accordance with more preferred teaching of the present invention, said temperature rise pattern is such that the temperature rise value is relatively high in a first half of battery charge and is relatively low in a second half of battery charge.
In accordance with more preferred teaching of the present invention, said temperature rise pattern is approximated polygonally.
In accordance with more preferred teaching of the present invention, said target temperature value is a value for completing the battery charge at the lowest temperature.
A battery charging method for making a battery side hold information on a target temperature value, which a battery is intended to reach, corresponding to charging time and charging the battery by means of a battery charger in accordance with the target temperature value, according to the present invention is characterized in that said battery charger comprises:
a storage device storing a temperature rise pattern for completing battery charge at the target temperature value read out from the battery side;
a temperature detecting section for detecting a present battery temperature;
a temperature rise pattern retrieving section for retrieving a temperature rise pattern from said storage device based on a battery temperature at the beginning of the battery charge and charging time;
a temperature rise value outputting section for obtaining a temperature rise value from the temperature detected by said temperature detecting section;
a current value retrieving section for retrieving a current value with which the temperature rise value outputted from said temperature rise value outputting section becomes said temperature rise pattern; and
a charge control section for charging the battery with the current value retrieved by said current value retrieving section.
In accordance with more preferred teaching of the present invention, said target temperature value is a value for completing the battery charge at the lowest temperature.
A battery is charged while adjusting a current value so that a temperature rise value may be constant. This makes it possible to charge the battery so that a battery temperature at the time of the completion of charge becomes a predetermined value. It is, therefore, possible to charge a nickel metal hydride battery or the like in a short time without overheating the battery.
A temperature rise pattern is retrieved from charging time based on the difference between a battery temperature at the beginning of battery charge and a target temperature value which the battery is intended to reach and which is held by a storage device. The battery is then charged while adjusting a current value so that a temperature rise value may become the temperature rise pattern. Due to this, by optimizing the temperature rise pattern, it is possible to charge the battery so that the battery temperature at the time of the completion of charge may become a predetermined value (i.e. a minimum temperature). It is, therefore, possible to charge a nickel metal hydride battery or the like, in a short time without overheating the battery.
A temperature rise pattern is generated based upon factors such as whether the difference between battery temperature and ambient temperature is small, the battery is difficult to cool, battery capacity is almost empty, temperature rise during battery is relatively small and a temperature rise value is relatively high in the first half of the battery charge. Conversely, the temperature rise pattern may be generated based upon factors such as whether the difference between the battery temperature and the ambient temperature is large, the battery is easily cooled, temperature rise during battery charge is relatively large and the temperature rise value is relatively low in the second half of the battery charge. That is, by setting the temperature rise pattern so as to optimize the various charging conditions, it is possible to charge the battery so that the battery temperature at the time of the completion of charge may be minimized.
Since a temperature rise pattern is approximated polygonally, processing such as arithmetic processing can be easily carried out.
A target temperature value which the temperature is intended to reach is a value for completing battery charge at the lowest temperature and allows charging the battery so that a battery temperature at the completion of charge may be minimized.
Further, since the battery side holds data on the target temperature value which the battery is intended to reach, it is possible to charge different types of batteries so that temperatures at the time of the completion of charge may become the target temperature values (the lowest temperatures), respectively. In various types of battery chargers, even a battery charger capable of quickly charging a battery in, for example, 15 minutes or that capable of charging a battery in one hour, it is possible to charge the battery so that the battery temperature at the time of the completion of charge may become the target temperature value which the battery is intended to reach (the lowest temperature).
Target temperature value which the battery is intended to reach is a value for completing battery charge at the lowest temperature and allows charging the battery so that the temperature at the time of the completion of charge may be minimized.
The present invention has been made to solve the above-stated problems and another embodiment of the invention is to provide a battery charger capable of appropriately charging a battery pack including many battery cells.
In another embodiment of the invention, a battery charger dividing and charging a battery consisting of a plurality of battery cells, comprises:
a storage device storing a map, in which an allowable current value, with which the battery can be charged while a temperature rise of the battery is being suppressed, is mapped based on a battery temperature value and a battery temperature rise value;
a temperature detecting section for detecting a present battery temperature;
a temperature rise value outputting section for obtaining the temperature rise value from the temperature detected by said temperature detecting section;
an allowable current value retrieving section for retrieving the map of said storage device based on the temperature detected by said temperature detecting section and the temperature rise value outputted from said temperature rise value outputting section, and for obtaining said allowable current value;
a charging section for charging said divided battery with the allowable current value retrieved by said allowable current value retrieving section; and
a charge switching section for alternately switching divided blocks to be charged by said charging section.
Another embodiment of a battery charger dividing a battery consisting of a plurality of battery cells into two or more blocks and charging the divided blocks, comprises:
a storage device storing a map, in which an allowable current value, with which the battery can be charged while a temperature rise of the battery is being suppressed, is mapped based on a battery temperature value and a battery temperature rise value, the allowable current value set at a low value if the battery temperature value is high and set at a low value if the temperature rise value is high;
a temperature detecting section for detecting a present battery temperature;
a temperature rise value outputting section for obtaining the temperature rise value from the temperature detected by said temperature detecting section;
an allowable current value retrieving section for retrieving the map of said storage device based on the temperature detected by said temperature detecting section and the temperature rise value outputted from said temperature rise value outputting section, and for obtaining said allowable current value;
a charging section for charging said divided battery blocks with the allowable current value retrieved by said allowable current value retrieving section;
a charge switching section for alternately switching the divided battery blocks to be charged by said charge section;
a charge completion determining section for determining completion of charge of each of the divided battery blocks based on whether frequency, with which the temperature detected by said temperature detecting section and the temperature rise value outputted from said temperature rise value outputting section belong to regions indicating a final charging period in the map of said storage device, is high; and
a charge completing section for completing charge of the divided battery blocks based on determination of completion of battery charge by said charge completion determining section.
Another embodiment of a battery charger capable of charging a battery consisting simultaneously of a plurality of battery cells and dividing the battery into two or more blocks and then charging the divided battery blocks, comprises:
a storage device storing a map, in which an allowable current value, with which the battery can be charged while a temperature rise of the battery is being suppressed, is mapped based on a battery temperature value and a battery temperature rise value;
a temperature detecting section for detecting a present battery temperature;
a temperature rise value outputting section for obtaining the temperature rise value from the temperature detected by said temperature detecting section;
an allowable current value retrieving section for retrieving the map of said storage device based on the temperature detected by said temperature detecting section and the temperature rise value outputted from said temperature rise value outputting section, and for obtaining said allowable current value;
a charging section for charging the battery with the allowable current value retrieved by said allowable current value retrieving section; and
a charge switching section for switching said charging section and charging the battery consisting of the plurality of battery cells simultaneously or charging the battery separately, wherein
said charge switching section simultaneously charges the battery consisting of the plurality of battery cells at beginning of battery charge, and alternately switches the divided battery blocks and charges the divided battery blocks in a final charging period.
Another embodiment of a battery charger dividing a battery consisting of a plurality of cells into two or more blocks and charging the divided battery blocks, comprises:
a storage device storing a map, in which an allowable current value, with which the battery can be charged while a temperature rise of the battery is being suppressed, is mapped based on a battery temperature value and a battery temperature rise value, the allowable current value set at a low value if the battery temperature value is high and set at a low value if the temperature rise value is high;
a temperature detecting section for detecting a present battery temperature;
a temperature rise value outputting section for obtaining the temperature rise value from the temperature detected by said temperature detecting section;
an allowable current value retrieving section for retrieving the map of said storage device based on the temperature detected by said temperature detecting section and the temperature rise value outputted from said temperature rise value outputting section, and for obtaining said allowable current value;
a charge switching section for switching said charging section and charging the battery consisting of the plurality of battery cells simultaneously or charging the battery separately;
a final charging period determining section for determining that a battery charge period is in a final charging period based on whether or not frequency, with which the temperature detected by said temperature detecting section and the temperature rise value outputted from said temperature rise value outputting section belong to regions indicating the final charging period in the map of said storage section, is high; and
a charge completion determining section for determining completion of charge of each of the divided battery blocks based on whether or not the frequency, with which the temperature detected by said temperature detecting section and the temperature rise value outputted from said temperature rise value outputting section belong to the regions indicating the final charging period in the map of said storage section, is high, wherein
said charge switching section simultaneously charges the battery consisting of the plurality of battery cells at beginning of battery charge and, if the battery charge period is determined to be in the final charging period by said final charging period determining section, alternately switches the battery divided by the charge switching section and charges the battery until said charge completion determining section determines the completion of charge.
Another embodiment of a battery charger obtains an allowable current value with which a battery can be charged while the temperature rise of the battery is being suppressed, by employing a map, in which the allowable current value is mapped based on a battery temperature value and a battery temperature rise value. That is, the battery charger retrieves the map based on the battery temperature and the temperature rise value, obtains the allowable current value with which the battery can be charged while the temperature rise of the battery is being suppressed, and charges the battery with the allowable current value. This makes it possible to charge the nickel metal hydride battery which temperature tends to rise during charge, in a short time without causing deterioration due to temperature rise. Since the divided battery cells are alternately switched, i.e., the battery cells in one block are charged while those in the other block are being cooled, it is possible to efficiently charge the battery even just before the completion of battery charge. A battery charger obtains an allowable current value with which a battery can be charged while the temperature rise of the battery is being suppressed, by employing a map, in which the allowable current value is mapped based on a battery temperature value and a battery temperature rise value. That is, the battery charger retrieves the map based on the battery temperature and the temperature rise value, obtains the allowable current value with which the battery can be charged while the temperature rise of the battery is being suppressed, and charges the battery with the allowable current value. This makes it possible to charge a nickel metal hydride battery which temperature tends to rise during charge, in a short time without causing deterioration due to temperature rise.
Particularly, charge completion is determined based on whether or not the temperature rise value is relatively high and the frequency, with which a relatively low allowable current value is outputted from the map, is high, i.e., whether or not temperature rise is large and temperature rise is still large even with a charging current value being lowered. Due to this, it is possible to 100% charge the battery without overcharging it irrespective of the residual capacity of the battery, temperature and the like. Further, since this battery charger determines the completion of charge by dividing the battery, it is possible to accurately determine the completion of charge compared with a case of simultaneously determining it for all battery cells.
Another embodiment of a battery charger obtains an allowable current value with which a battery can be charged while the temperature rise of the battery is being suppressed, by employing a map, in which the allowable current value is mapped based on a battery temperature value and a battery temperature rise value. That is, the battery charger retrieves the map based on the battery temperature and the temperature rise value, obtains the allowable current value with which the battery can be charged while the temperature rise of the battery is being suppressed, and charges the battery with the allowable current value. This makes it possible to charge a nickel metal hydride battery which temperature tends to rise during charge, in a short time without causing deterioration due to temperature rise. Further, since all the battery cells are simultaneously charged at the beginning of battery charge in which lower heat generated and then the battery cells are charged while dividing the battery and alternately switching the charge target battery cells, i.e., the battery cells in one block are charged while those in one block are being cooled in the final charging period in which high heat is generated, it is possible to efficiently charge the battery in a short time.
Another embodiment of a battery charger obtains an allowable current value with which a battery can be charged while the temperature rise of the battery is being suppressed, by employing a map, in which the allowable current value is mapped based on a battery temperature value and a battery temperature rise value. That is, the battery charger retrieves the map based on the battery temperature and the temperature rise value, obtains the allowable current value with which the battery can be charged while the temperature rise of the battery is being suppressed, and charges the battery with the allowable current value. This makes it possible to charge a nickel metal hydride battery which temperature tends to rise during charge, in a short time without causing deterioration due to temperature rise. Further, since all the battery cells are simultaneously charged at the beginning of battery charge in which lower heat generated and then the battery cells are charged while dividing the battery cells and alternately switching the charge target battery cells, i.e., the battery cells in one block are charged while those in the other block are being cooled in the final charging period in which high heat is generated, it is possible to efficiently charge the battery in a short time.
Particularly, final charging period is determined based on whether or not the temperature rise value is relatively high and the frequency, with which a relatively low allowable current value is outputted from the map, i.e., whether or not temperature rise is large and temperature rise is still large even with a charging current value being lowered. Due to this, it is possible to appropriately judge timing for switching charge operation to division charge and to efficiently shorten charging time. Besides, charge completion is determined based on whether or not the temperature rise value is relatively high and the frequency, with which a relatively low allowable current value is outputted from the map, is high. Due to this, it is possible to 100% charge the battery cells without overcharging it irrespective of the residual capacity of the battery, battery temperature and the like. Further, since this battery charger determines the completion of charge by dividing the battery, it is possible to accurately determine the completion of charge compared with a case of simultaneously determining it for all battery cells.
A more detailed explanation of the invention is provided in the following description and appended claims take in conjunction with the accompanying drawings.